1. Field of the Invention
This invention relates to alginates, and in particular, to methods of placing water-soluble alginates in liquid form.
2. Description of the Related Art
Alginates are hydrocolloids which are commercially extracted from brown marine microalgae. Water soluble alginates are widely used in many industries, e.g., paper, textiles, paint, oil drilling, pharmaceuticals and food. For instance, in small percentages they are found in high solids paper coatings and textile print pastes as rheological control (thickening) agents. Alginates are also widely used in foods such as frozen deserts, salad dressings, dairy products, bakery products and beverages. Many of the applications for these industrial systems are fully automated with the exception of feed systems for alginates which utilize an eductor (FIG. 1) or a dry feeder, both of which systems are subject to clogging. In addition, using an eductor can be cumbersome.
Alginates are commonly furnished in granular form, with the particle size generally ranging from as coarse as 20 mesh (U.S. standard sieve) to about 200 mesh. The hydrophilic nature of these polysaccharide gums which make them useful thickening agents, leads to difficulty when such polymers are added to water. There is a tendency for the individual particles to undergo surface swelling and stick to each other, generally trapping air inside an aggregate of the partially swollen granules. These aggregates, or "lumps," are very difficult to redisperse because the entrapped bubbles resist the penetration of water, and it is difficult for water to penetrate into the interior of a lumpy aggregate.
Previously, the alginates have had to be added as dry powders which was inconvenient for the end users of the product. To obtain a pumpable product and yet avoid the problem of trying to suspend alginates in water, other types of suspensions or dispersions have been tried. For example, in the patent of Colgrove (U.S. Pat. No. 3,894,880) an alginate is dispersed in water and alcohol using 0.3-1.0% xanthan gum as the suspending agent. Xanthan gum is a hydrophilic colloid. About 12-28.5% isopropanol was found to provide a blend of satisfactory viscosity. There are disadvantages to using non-aqueous solvents such as alcohol, including flammability, toxicity, possible environmental problems, and interference with uses of the alginate.
Another liquid thickener which is being used in the textile and paper industries is an alkali-swellable synthetic polymer, ALCOGUM.TM. (Alco Chemical Corporation). Although its rheological and water retention properties are similar to that of alginates, its chemistry and functionality are quite different. The ALCOGUM.TM. products are emulsions and not suspensions, which are synthesized by polymerizing methacrylic acid and ethylacrylate to yield polymers of varying properties. Due to their chemistry the ALCOGUM.TM. products require alkali to activate their viscosity functionality. Ammonia is the usual base used to neutralize the acid groups and promote swelling. These products have the disadvantages that in addition to requiring the handling of ammonia, the products are in the form of lattices and lose their functionality when frozen. The frozen polymeric product contains trace amounts of toxic monomers, presenting a disposal problem. The products are also not biodegradable.
It is therefore an object of this invention to provide a pumpable suspension of a soluble alginate which can be easily used in an automated plant. It is a further object to provide a process for preparing a pumpable alginate suspension. Another object is to provide an alginate suspension which is non-toxic, nonflammable, freeze resistant, biodegradable, and does not contain any substances which interfere in the alginate application.
Other objects and advantages will be more fully apparent from the following disclosure and appended claims.